Application of CFD and FEA Coupling to Predict Structural Dynamic Responses of A Trimaran in Uni-and Bi-Directional Waves

To predict the wave loads of a flexible trimaran in different wave fields,a one-way interaction numerical simulation method is proposed by integrating the fluid solver(Star-CCM+)and structural solver(Abaqus).Differing from the existing coupled CFD-FEA method for monohull ships in head waves,the presented method equates the mass and stiffness of the whole ship to the hull shell so that any transverse and longitudinal section stress of the hull in oblique waves can be obtained.Firstly,verification study and sensitivity analysis are carried out by comparing the trimaran motions using different mesh sizes and time step schemes.Discussion on the wave elevation of uni-and bi-directional waves is also carried out.Then a comprehensive analysis on the structural responses of the trimaran in different uni-directional regular wave and bi-directional cross sea conditions is carried out,respectively.Finally,the differences in structural response characteristics of trimaran in different wave fields are studied.The results show that the present method can reduce the computational burden of the two-way fluid-structure interaction simulations.

Numerical Prediction of Form Factor and Wave Interference of A Trimaran for Different Outrigger Positions

Trimaran hydrodynamics have been an important research topic in recent years.Trimarans have even been chosen for naval surface combatants.In this case,investigation of a trimaran with different outrigger positions is important and necessary for better hydrodynamic performance.This paper focuses on the numerical investigation of trimaran hydrodynamics.The trimaran model used in this study is a 1/80 scale high-speed displacement frigate-type concept developed by the Center for Innovation in Ship Design(CISD)at Naval Surface Warfare Center,Carderock Division(NSWCCD).The numerical simulations were conducted for different outrigger positions at low and moderate Froude numbers by using commercial CFD software solving URANS equations.A verification and validation study was carried out for the numerical method in one configuration and one ship velocity.The existing experimental results for the trimaran resistance in the literature were used for validation.Five different outrigger positions were analyzed and the form factor of each configuration was calculated by the Prohaska method.The total resistance was decomposed to its components using the form factor.The interference factor was calculated for each configuration in terms of total resistance,residual resistance and wave resistance.Also,wave profiles using the longitudinal wave cuts in different locations were obtained both numerically and experimentally.It was concluded that the outrigger position had different effects on the interference,total resistance and wave profile at different Froude numbers.It was also shown that the CFD results were in good agreement with the experimental data in all configurations.In conclusion,this study presents the results of interference effects for different trimaran configurations in terms of wave resistance in addition to the total resistance and residual resistance.The numerical method was validated not only with the total resistance test data but also the longitudinal wave profiles along the hull.

Resistance Analysis of Unsymmetrical Trimaran Model with Outboard Sidehulls Configuration

河和海环境里的运输的一个模式在最近的年里很快成长了的多壳轮船或三个船体并列的游艇容器的申请。三个船体并列的游艇容器由于能被完成的水动力学效率的高水平当前具有为许多新高速度轮船工程的兴趣，与相比单音壳并且长筏壳表格。这研究的目的是识别与配置(S/L ) 使用一个不对称的三个船体并列的游艇轮船模型的可能的效果 0.10.3 并且 R/L=0.10.2。有主要尺寸的不对称的三个船体并列的游艇轮船模型：L=2000mm， B=200 公里和 T=45 公里。试验性的方法(拖引的坦克) 在第 0.10.6 期弗鲁德点用速度变化在学习被执行。轮船模型被其速度能被改变并且调整的一台电动机拉。轮船模型抵抗被使用一个负担房间变换器精确测量。为每种配置与的轮船抵抗的比较单音壳作为全部的抵抗系数和弗鲁德数字的功能在图上被显示出。测试结果发现有效拖减小能与配置 S/L=0.1 在 Fr=0.35 被完成直到 17% 。

Numerical Research on Wave-making Resistance of Trimaran

A 3D rankine panel method was developed for calculating the linear wave-making resistance of a tri-maran with Wigley hulls. In order to calculate the normal vector and derivative of the body surface accurately, non-uniform rational B-spline (NURBS) was adopted to represent body surface and rankine source density. The radiation condition is satisfied using the numerical technology of staggered grids. Numerical results show that the linear wave-making resistance of the trimaran can be calculated effectively using this method.

Grid convergence study in the resistance calculation of a trimaran

As a new type of hull form,trimaran has remarkable excellent performances and has drawn more and more attention.When the viscous CFD technology now available is applied to the research of resistance performance of trimaran,the spatial discretization would usually result in the grid error and uncertainty,and thus the considerable discrepancy between the numerical results and the experimental data.In order to ascertain how much the grid would affect the calculation,the grid convergence should be studied.A mathematical trimaran was chosen as an example,with the commercial code CFX for the simulation,VOF for surface treatment,and the grid study was carried out based on two different turbulence models.It was concluded that carrying out grid study is helpful in estimating the grid error and uncertainty,and indicating the direction of improving the credibility of the numerical calculation, and,in addition to grid errors and uncertainties,the turbulence modeling errors and uncertainties contribute to the simulation errors.

STUDY OF TRIMARAN WAVEMAKING RESISTANCE WITH NUMERICAL CALCULATION AND EXPERIMENTS

Based on the potential flow assumption, this paper outlines the formulation of the boundary-value problem governing the steady free surface flow around a trimaran advancing at a constant forward. A Rankine panel method was developed for the solution of the problem. The side-hulls were treated as lifting bodies and circulation was introduced into the flow field to implement the asymmetrical flow around each side hull. The linearized free surface condition was used. The appropriate treatment for transom-stern ship was also discussed. Additionally, a test was performed to quantify the resistance and especially the interference between the main and side hulls. The numerical results are in good argeement with experimental data.

NUMERICAL SIMULATION OF WAVE RESISTANCE OF TRIMARANS BY NONLINEAR WAVE MAKING THEORY WITH SINKING AND TRIM BEING TAKEN INTO ACCOUNT

Up to now, there are no satisfactory numerical methods for simulating wave resistance of trimarans, mainly due to the difficulty related with the strong nonlinear features of the piece hull wave making and their interference. This article proposes a numerical method for quick and effective calculation of wave resistance of trimarans to be used in engineering applications. Based on Wyatt＇s work, the nonlinear free surface boundary condition, the time domain concept, and the full nonlinear wave making theory, using the Rankine source Green function, the 3-D surface panel method is expanded to solve the trimaran wave making problems, with high order nonlinear factors being taken into account, such as the influence of the sinking and trim, transom, and ship wave immersed hull surface. And the software is successfully developed to implement the method, which is validated. Several trimaran models, including a practical trimaran with a sonar dome and the transom, are used as numerical calculation samples, their wave making resistance is calculated both by the present method and some other methods such as linear （Dawson） methods. Moreover, sample model resistance tests were carried out to provide data for comparison, validation and analysis. Through the validation by model experiments, it is concluded that present method can well predict the wave making resistance, sinking and trim, and the accuracy of wave making resistance calculation is significantly improved by taking the trim and sinking into account, especially at high speeds.

Numerical and experimental analyses of hydrodynamic performance of a channel type planing trimaran

This paper studies the hydrodynamic performance of a channel type planing trimaran. A numerical simulation is carried out based on a RANS-VOF solver to analyze the hydrodynamic performance of the channel type planing trimaran. A series of hydrodynamic experiments in towing tank were carried out, in which both the running attitude and the resistance performance of the trimaran model were recorded. Some hydrodynamic characteristics of the channel type planning trimaran are shown by the results. Firstly, the resistance declines significantly, with the forward speed across the high-speed resistance peak due to the combined effects of the aerodynamic and hydrodynamic lifts. Secondly, the resistance performance is influenced markedly by the longitudinal positio- ns of centre of the gravity and the displacements. Besides, the pressure distribution on the hull and the two-phase flow in the channel are discussed in the numerical simulations.

A NUMERICAL STUDY ON SIDE HULL OPTIMIZATION FOR TRIMARAN

Due to the interaction between the main hull and side hulls, different layouts and lengths of side hulls affect the wave loads significantly. Based on three-dimensional potential theory and Green＇s function, this article gives the significant values for wave loads, including vertical shear forces and vertical bending moments at different locations on the main hull, and transverse bending moments at the junction of the cross structure and main hull. In addition, a parametric optimization of wave loads for different layouts and lengths of side hulls were perfomed. Several speeds and wave headings were also considered. Finally, spectral analysis was conducted to attain load distribution. The conclusions of this study are conducive to the design and optimization of this new type of ship

基于CFD的三体船主侧体间流场干扰研究

三体船构型复杂,主侧体间相互干扰影响因素较多。为了研究三体船船体周围流场细节与主侧体间的流场干扰,运用计算流体力学(CFD)软件STAR-CCM+对三体船和主船体进行了不同航速的数值模拟,提取船体周围与主侧体间的流场信息,获得不同速度下的兴波、横截面垂向速度和横截面矢量流线演化。研究三体船与单体船的流场差异特性,分析三体船中侧体对单独主船体流场的扰动,获得了三体船船体兴波与流场流线随航速变化的规律,为三体船的阻力性能和整体布局的优化提供参考。

基于四自由度的三体船操纵运动数值模拟研究

文中针对某高速三体船的操纵运动预报,开展约束模型试验和横摇衰减试验.基于MMG模型,获取四自由度操纵水动力导数,进行三体船回转运动及Z形操纵运动预报.在数值计算过程中,进行了网格尺度及时间步长的收敛性分析,探讨了纵摇和垂荡运动对数值模拟结果的影响;数值模拟了斜拖、旋臂、横倾及横摇衰减试验.基于最小二乘法拟合计算结果并得到水动力导数,结合四自由度MMG模型进行了不同舵角下三体船的操纵性能预报,得到了三体船的操纵性能参数.

基于CFD的排水型三体无人艇阻力优化研究

为预报某三体无人艇的静水航行阻力,利用STAR-CCM+软件对船体进行计算流体动力学仿真。基于船体的航速和排水量等设计参数,考虑侧体纵向位置和侧体船型2种因素,选取不同设计方案进行计算。结合后处理得到的流场特征对仿真结果进行分析,总结阻力变化规律,探讨船体水动力性能的变化机理。结果表明:侧体纵向位置后移可减小片体间兴波扰动,减阻率最大约6.7%;改变侧体型宽会小幅度降低船体压阻,其最大减阻率约4.5%。汇总多种船型方案的计算结果,为三体无人艇的后续研究提供参考。

三体船压浪板虚拟仿真系统

三体船压浪板作为完善船舶结构、降低船舶阻力的重要手段,在近年来得到了广泛的关注及应用,很好解决了船体航行中较大的纵向摇荡运动。本文通过对三体船的运动及受力进行分析,建立压浪板力学模型,采用数值计算与仿真技术相结合的方法,开发基于虚拟现实技术的三体船压浪板设计与分析系统。

船载波浪发电设备设计及其性能研究

为解决小型无人船由于船体空间紧凑,携带燃料较少导致的续航力差、航程短等问题,本文以三体船为平台,将摆式波浪能发电技术与多体船相结合,提出了一种新型船载波浪发电设备设计方案。该发电设备可由主侧船体之间的波浪运动响应差异驱动,在海上航行时捕获波浪能并转化为电能,以此来补充船上能源。通过数值软件对三体船进行性能预报,结果表明,在四级海况下迎浪航行时,三体船平均波浪能捕获功率可达3.57 kW,波浪能一级转换效率为7.32%,能够有效地补充船上能源。同时,安装船载波浪发电设备具备减摇减荡的效果,提升了三体船的航行稳定性,进一步体现了该装置的可行性和实用性。

三体船操纵性自航回转运动仿真预报分析

针对船舶操纵性自航回转试验成本较高,且现有成熟仿真方法效率低、分析要素单一等问题,本文提出了一种船舶自航回转运动数值模拟方法,并利用商用计算流体力学软件Star-CCM+对三体船模在满舵角30°和半舵角15°所受推力情况下的自航回转运动进行了数值模拟,将该模拟结果与较为成熟的基于数学模型方程组的约束模仿真回转运动结果进行了对比分析,通过对三体船在满舵角和半舵角时的纵距、横距、旋回初径和回转直径等操纵性回转要素值进行分析可知,其差值均在7%以内,验证了文中所提方法的可靠性。且采用文中所提方法对目标船模进行模拟计算时,不仅能够获得船模在平面运动内的回转性能要素,同时还能得到船模横摇、纵摇、升沉等多自由度运动响应要素,本文亦对三体船在满舵角和半舵角下做自航回转运动时的横摇、纵摇、升沉等响应要素进行了分析,从定性分析的角度看,模拟所得的各运动响应要素结果与实际船舶在做回转运动时产生的现象相符;从定量的角度分析,模拟目标船模所得各运动响应要素结果较好,不会对船模回转产生较大干扰。

相控阵三体折叠船风动遥控改造及其在流量测验中的应用

为了使相控阵ADCP三体折叠船具有遥控自动测流,在不破坏相控阵三体折叠船的基础上,利用风动技术进行遥控改造。改造后的三体折叠船在遥控流量测验应用中取到了良好效果。介绍了相控阵ADCP三体折叠船风动遥控改造的总体设计、改造方法和应用情况。

某内河三体船轴流式喷泵台架试验与性能计算

为检验某内河三体船的轴流式喷泵性能,开展缩比模型试验泵台架试验。采用结构化网格离散计算域得到实尺度喷泵外特性曲线,经无量纲相似换算得到与试验情况相符合的计算流体力学(Computational Fluid Dynamics, CFD)计算值。在流量阀全打开、非等转速条件下和不同流量、等转速条件下进行测量,得到试验泵功率和扬程等数据。在功率损失分析基础上,对比试验测量值与CFD计算值。结果表明:在1 130~1 760 r/min转速条件下两者吻合较好,最大误差为7.6%;在等转速条件下扬程特性曲线趋势达成较好一致性。

基于VLIW DSP的可重定向编译器设计与实现

本文给出了一种基于VLIWDSP的快速移植编译器的方法,详细讨论了Trimaran架构中的关键技术:Elcor、模拟器以及定制目标机指令和操作码,成功移植了基于BWDSP100芯片单簇体系结构的编译器,很大程度上缩短了开发周期。

超细长三体船耐波性试验研究

通过三体船模型耐波性试验,包括横摇试验、规则波中的迎浪试验,研究了侧体布置位置和舭龙骨对三体船横摇运动的影响以及在波浪中的纵摇和垂荡运动特点。